Made as of the early 18^th century, regulators are extremely accurate timekeepers that were generally used to provide the correct time when setting clocks and wall cartels. Their appearance was directly linked to the scientific progress made during the Age of Enlightenment, which led to significant improvements in time measurement and made horology an important field of study.

In this article we will examine three major inventions that are inseparable from regulators: the equation of time, the compensated pendulum, and the remontoire, or constant force device. These inventions laid the technological foundations for precision, and still influence creators of haute horology today.

Equation of Time

For a long time human activities were organized according to the Sun. The systematic observation of the Sun laid the basis for the essential notions of time. Thus, the interval between two successive passages of the Sun along the same meridian defined the length of the day – i.e., the solar day. That length, however, may vary greatly due to the Earth’s elliptical trajectory, which affects its speed (slowest at the aphelion and fastest at the perihelion), and the angle of the rotational axis of the Earth.

While this variation was known by the Middle Ages, it only began to cause problems during the 17^th century, as the first relatively accurate clocks began to be made. When their owners tried to set them with the aid of a sundial, they soon realized the time indicated by the clock and that shown by the sundial varied constantly in relation to one another.

Since a clock’s rate could not be easily modified over the course of a year, the system of equal hours – i.e., mean time, was devised and gradually applied. This consists in attributing a fixed value to each day and dividing and distributing the remaining variations of the solar days.

Mean time and true time coincide four times a year, in mid-April and mid-June, and in late August and December. The rest of the year, the Sun is either ahead or behind the clock. That gap, approximately 15 minutes in length, is called the equation of time. By the second half of the 17th century, clockmakers had begun to establish accurate tables quantifying the equation of time, to facilitate the conversion. One such table was published by Christian Huygens in 1665.

Since clocks were commonly adjusted according to the equation of time (fig. 1), during the early decades of the 18^th century clockmakers devoted themselves to creating clocks that were able to display it. This led to the creation of the first longcase regulators.

Fig. 1 – *Tables of Equations of the sun’s movement (Tables des Équations du mouvement du soleil)*, calculated by Claude IV Railliard and dated 1718, an excerpt of which was published by Antoine Thiout in his horological treatise.

Appointed clockmaker to the king (horloger ordinaire du Roi) in 1739 and invited to live and work in the Galeries du Louvre, Julien Le Roy (1686-1759) was one of the most eminent horologists who studied the problem of the equation of time. He made dials with turning disks that indicated the equation of time and the date, either through apertures (fig. 2) or by means of arrows placed around the dial (fig. 3).

Fig. 2 – Dial of a longcase regulator by Julien Le Roy (detail), Paris, Louis XV period, circa 1730. Made of silvered metal, it is signed “Invented in 1730 by Julien Le Roy of the Société des Arts” (“Inventé en 1730 par Julien Le Roy de la Société des Arts”). The outer portion indicates true time by means of two gilt hands, the minute hand being adorned with a sunray mask. It has two apertures below, which show the date and the corresponding equation of time.

Fig. 3 – Dial of a longcase regulator by Julien Le Roy with case by Charles Cressent (detail), Paris, Louis XV, period, circa 1750. It is signed “Julien Le Roy A.D. (“Ancient Directeur”, or Former Director) of the Société des Arts”. A revolving ring bearing the date and solar minutes is placed on the outside of the main dial. As the ring turns, following the minute hand, a fixed arrow indicates the corresponding date. The equation of time is obtained by noting the gap between the solar and mean time minutes, indicated by the same hand.

The system was simplified during the second half of the 18^th century, due to the emergence of entirely enameled dials, as well as to the prevailing fashion favoring a more sober style influenced by classical antiquity. One fine example was made by Robert Robin (1742-1799) in 1776 (fig. 4).

Fig. 4 – Dial of a floor regulator by Robert Robin, in a rosewood and amaranth-veneered case by Balthazar Lieutaud (detail), Paris, early Louis XVI period, 1776. The finely enameled dial by Elie Barbezat indicates the mean time. The inner disk, which turns in relation to the position of the minutes hand, indicates the solar minutes similarly to the Le Roy device, but with a more modern treatment.

Entirely enameled dials allowed the use of ever-more sophisticated decorative schemes. Additional indications could be added, along with beautiful embellishments; these might include the date, the calendar, and the Zodiac signs, and gradually led to the disappearance of the equation disc. Instead, most regulators of the Louis XVI period were fitted with two minute hands. Made respectively of gilt bronze and steel, the first hand indicated the solar minutes while the second showed the mean time minutes. This remained the general practice until the Empire period (fig. 5).

Fig. 5 – Dial of a floor regulator by Pierre-Basile Lepaute (1750-1843), enamel by Dubuisson (1731-1815), in a mahogany case (detail), Paris, Empire period, circa 1805. The solar minutes are shown by a gilt bronze hand adorned with a sun mask, the mean time minutes are indicated by a steel hand. The lower aperture contains the Republican and Gregorian annual calendars.

Compensated Pendulum

Very early on, clockmakers realized that temperature variations had a significant impact on the rate of clocks. Thermal variations caused the pendulum to expand and contract and led to constant changes in its length, which caused the clock to run either fast or slow. By the early 18^th century, research was carried out to solve this problem, leading to the construction of pendulums that compensated for differences in temperature. One leading horologist who performed research in this field was George Graham, who invented pendulums with vials filled with mercury around 1720 (fig. 6).

**Fig. 6 – Mercury compensation pendulum tested by George Graham around 1727. British Museum.**

Initially Graham’s trials included steel and brass, however he quickly eliminated them, for the expansion coefficients of the two metals were too close to cancel each other out. Around 1725, John Harrison continued Graham’s research, eventually coming up with a pendulum in which two metals, fashioned into rods, were laid out in a grid form and were linked together by several cross pieces (fig. 7). As the steel rods lengthened under the effect of heat and drew the pendulum downward, the brass rods, which had a higher coefficient, pushed the cross pieces upward. Thus, the two tendencies cancelled each other out, allowing the pendulum to maintain a constant center of gravity.

**Fig. 7 – Drawing of a gridiron pendulum from John Harrison’s 1730 manuscript.**

Widely disseminated throughout Europe, John Harrison’s gridiron pendulum was particularly successful in France. During the 18^th century, nearly all French regulators were equipped with it (fig. 8). A thermometer was sometimes included to indicate the temperature, based on the expansion of the metals (fig. 9). It was not until the first half of the 19^th century that mercury pendulums came to be widely used.

Fig. 8 – Gridiron pendulum of a skeleton desk regulator by Jacques-Joseph Lepaute (detail), Paris, Louis XVI period, circa 1783. The beauty of the pendulum is showcased by the sober design of the clock, as well as by its large bob, both made of finely chased and gilt bronze. The back plate bears the inscription: “Lepaute de Bellefontaine horloger de Monsieur à Paris” (“Lepaute of Bellefontaine clockmaker to Monsieur in Paris”), indicating the clockmaker worked for “Monsieur”, the Count de Provence and brother of King Louis XVI.

Fig. 9 – Gridiron pendulum of a floor regulator by Jean-Simon Bourdier (detail), Paris, late Louis XVI period, circa 1785-1790. The thermometer is fixed to the bob, which was made according to the theories of John Ellicott.

Remontoire

Though very complex and difficult to put in place, the remontoire or constant force device (“remontoir d’égalité” in French), allows the energy of the spring to be converted into a force like that furnished by a weight. This naturally increases accuracy, for even when fitted with a fusée, a spring inevitably loses energy as it unwinds. This problem was almost entirely solved by the remontoire, which transfers the spring’s energy to a small weight. The latter, in turn, supplies its driving force to the mechanism. Each time the weight descends to its lowest point, the spring brings it back to its starting position.

This device was perfected by clockmaker Robert Robin (1742-1799), who in 1772 submitted his idea to the French Royal Academy of Sciences in a “memoir containing reflections on the properties of the remontoir”. The device made Robin famous. The invention was so influential that Louis Moinet devoted entire passages of the book he published several decades later to Robin’s remontoire. (fig. 10)

**Fig. 10 – Drawing of Robert Robin’s remontoir d’égalité, illustrated in Louis Moinet’s horological treatise.**

Perfectly suited to small-sized clocks while offering maximum precision, the remontoire made it possible to produce desk regulators, of which Robin was the true creator. Housed in cases that were entirely glazed, Robin’s clocks allowed connoisseurs to freely examine and admire the delicacy and technical prowess of their movements, which were specially conceived for each individual clock, and always feature individual variations. Their cases, however, remain quite similar. Generally featuring clean and simple lines and made of gilt bronze, their main purpose was to protect and showcase the mechanism, while displaying the characteristics of the prevailing fashions of the day.

Fig. 11 – Remontoir d’égalité of a desk regulator signed ”Cronier Jeune élève de Robin” (“Cronier the younger, student of Robin”) Paris, Consulate period, dated 1800. Though the few known pieces that bear this signature are all masterpieces, very little is known about the life of this mysterious clockmaker. We can safely assume he was one of Robert Robin’s most gifted students.

Other clockmakers constructed their own desk regulators based on those of Robin. The most talented among them also employed remontoires, which were always constructed in the same manner. This was the case for Cronier Jeune, a student of Robin’s (fig. 11), and for Lepaute. The latter was mentioned in the registers of the Imperial Garde-Meuble in 1808, in connection with the delivery to the Palace of Saint-Cloud of a regulator with remontoire. That clock (fig. 12) was housed in a case similar to the ones Robin had used two decades earlier.

Fig. 12 – Desk regulator with remontoir d’égalité, delivered by Lepaute in 1808 for the sum of 1500 francs, to be placed in the crimson salon of the Emperor’s small apartments in Saint-Cloud Palace. Paris, Mobilier national.

Y. Huang

Our previous article offered a general introduction to the horological creations of the reign of Louis XVI, and discussed several typical models. Since the reign of Louis XVI was extremely rich in terms of artistic creation, we wished to devote an entire article to one particular type of timepieces: porcelain clocks. These were the most fashionable and desirable objects one could dream of possessing in the late 18^th century.

Early Models: from Vincennes to Sèvres

The earliest porcelain clocks appeared during the reign of Louis XV. As early as 1749, the archives of the Vincennes Manufactory mention a porcelain clock delivered to “Monsigneur le Contrôleur Général”, Jean-Baptiste Machault d’Arnouville. However, such clocks were very scarce, and often involved the use of different types of porcelain. This is the case for the clock known as “the Concert of the Monkeys” (fig. 1), which featured soft-paste porcelain flowers from Vincennes and hard-paste porcelain figurines from Meissen.

Fig. 1 – The “Concert of the Monkeys” clock, movement by Jean Moisy; gilt bronze mounts by Jean-Claude Chambellan, known as Duplessis; Vincennes and Meissen porcelain, circa 1755-1760. Paris, Petit Palais.

Transferred to Sèvres in 1756, the Vincennes manufactory, which enjoyed the patronage of the king, became the Royal Sèvres manufactory, with exclusive rights to the production of hard-paste porcelain. As of the 1760s, Sèvres began making clock cases in greater numbers. We know that a clock with “pieds de biches” and “petit vert” decoration was delivered in 1762 to Madame de Pompadour. That clock is today in the Musée du Louvre (inv. OA10899).

The Triumph of Sèvres

During the reign of Louis XVI, porcelain was a highly fashionable material for luxury items. Gilt bronze was often used to increase the elegance of these pieces. Their forms considerably evolved and diversified thanks to the marchands-merciers, who were always seeking to offer ever-more fashionable objects to their sophisticated and demanding clients. Among them, Simon-Philippe Poirier and his associate, and later successor, Dominique Daguerre are particularly noteworthy. The latter enjoyed a near monopoly on the sale of Sèvres porcelain. For example, Sèvres sold him nearly all (thirty-two pieces) of its truncated columns, a great number of which were then mounted as clocks.

The series of truncated columns was particularly appreciated by the royal family, for Poirier had already delivered one, “adorned with porcelain figures”, to Madame du Barry in 1771; she gave it to the Count and Countess de Provence as a wedding gift. The Count d’Artois purchased another with gilt figures for the Turkish cabinet in the Palais du Temple. It stands today in the Château de Versailles (fig. 2).

Fig. 2 – Truncated column clock in Sèvres porcelain, movement by Charles Dutertre, Paris, Louis XVI, period, circa 1775. Delivered by Simon-Philippe Poirier to the Count d’Artois in 1777. Musée National du Château de Versailles (inv. VMB 889).

Daguerre’s boutique was one of the most popular attractions for Parisians and the elites of foreign countries. “You could hardly get close to his shop, because of the crowds of people that flocked around it”, said the Baroness of Oberkirch, who accompanied the Countess du Nord on a visit to Paris in 1782. The countess was following her husband, Tsarevitch Paul of Russia, on a grand tour of Europe. At Daguerre’s boutique the princely couple purchased this celebrated clock adorned with Sèvres porcelain plaques (fig. 3), which is today in the Rijksmuseum.

Fig. 3 – Gilt bronze mantel clock with Sèvres porcelain plaques, movement by Louis Montjoye, Paris, Louis XVI period, 1782. Purchased by Tsarevitch Paul, the future Paul I, it stood in Pavlovsk Palace. This clock was seized during the Russian Revolution and was sold in 1932 along with other pieces from the imperial collection. Amsterdam, Rijksmuseum.

The same model features in the catalogue of items that Daguerre presented to the Duke of Saxony-Teschen and Archduchess Maria Christina of Austria (fig. 4), who at the time were furnishing the Château de Laeken, their residence in Brussels. With a movement by Sotiau and also dated 1782, this clock is one of the most prestigious masterpieces currently offered by La Pendulerie (fig. 5).

**Fig. 4 – *Drawing of a bronze and porcelain clock*, Paris, circa 1782. New York, Metropolitan Museum of Art.**

Fig. 5 – Gilt bronze mantel clock with Sèvres porcelain plaques, movement by Sotiau, Paris, Louis XVI period, 1782. Probably delivered by Dominique Daguerre to the Duke of Saxony-Teschen, circa 1785. © La Pendulerie – Agence Phar

In addition to the plaques decorating clocks, vase-form clocks or “vases à monter” constitute a specific category of the items made at Sèvres. Often furnished with gilt bronze mounts, they sometimes feature a circular dial. Some of the more exceptional pieces have a cercles tournants dial. Sold initially by Poirier and later by Daguerre, many of them were fitted with movements by Charles Dutertre (d. before 1778), who was Poirier and Daguerre’s main supplier as of 1771. (fig. 6).

Fig. 6 – Gilt bronze vase clock with Sèvres porcelain plaques, movement by Dutertre, Paris circa 1770. Probably formerly in the collection of Sir Anthony de Rothschild (1810-1876). © La Pendulerie – Agence Phar

Lyre clocks are undoubtedly among the best known models made by the Sèvres manufactory. As mentioned in the preceding article, Louis XVI acquired two examples from the manufactory in 1785. At the end of each year, Sèvres organized an exclusive exhibition at which new models were presented to the royal family. Many of these were purchased at the factory, and the remaining pieces were sold by the marchands–merciers, who offered them only to their wealthiest clients.

As concerns lyre clocks, the Sèvres archives mention only thirty or so examples that were made between 1786 and 1797, all in four colors: bleu nouveau, turquoise, green and pink (fig. 7). They were so successful that the model continued to be produced during the 19^th century by other factories, including the Locré or Pouyat et Russinger factory, which made a unique replica that must have been produced on special order (fig. 8).

**Fig. 7 – Pink Sèvres porcelain lyre clock, movement by Dieudonné Kinable, polychrome enamel by Dubuisson, Paris, circa 1785-1790. © La Pendulerie – Agence**

**Fig. 8 – Celadon green Locré porcelain lyre clock, movement by Dieudonné Kinable, enamel by Dubuisson, Paris, circa 1815-1820. © La Pendulerie – Agence**

Rivals of Sèvres: Private Manufactories

Nevertheless, Sèvres was not the only manufactory to produce porcelain clock cases during the reign of Louis XVI. Though small, the manufactory in rue Thiroux, which was founded towards the end of the 1770s by André-Marie Leboeuf, was one of Sèvres’ main rivals. That manufactory was known for its extremely elegant decorative motifs, which drew the attention of Marie-Antoinette, who soon became an appreciative client.

In 1778 Leboeuf obtained the queen’s patronage, which would allow his enterprise to bear the name of “the Queen’s manufactory”. His wares were sold by the famous marchand-mercier Charles Raymond Granchez, who was the appointed supplier of jewelry and other adornments to Marie-Antoinette. He promoted the manufactory’s new products in his boutique. In the Cabinet des Modes of January 1786, Granchez published the drawing of a “Desk clock … in porcelain from the Queen’s manufactory (that) is in the form of a vase decorated with scattered flowers…” (fig. 9).

Fig. 9 – Mantel garniture comprising a clock and two porcelain candlesticks made by the Queen’s Manufactory and sold in Granchez’ boutique *Au Petit Dunkerque*. *Cabinet des Modes*, January 1, 1786, plate III.

An example of this model, the only one known to date (fig. 10) is currently offered by La Pendulerie. Its dial bears the signature “Godon à Paris”, which is that of François-Louis Godon. Godon’s signature also appears on other clocks made by the Queen’s Manufactory. This is the case for the clock known as “the Queen’s clock” (fig. 11). Signed “Godon, Relojero de Camara”; it was no doubt made after 1786, the year that Godon began to work for the Prince of Asturias, the future Charles IV of Spain.

**Fig. 10 – Porcelain and gilt bronze clock, case by the Queen’s Manufactory, movement by François-Louis Godon. Paris, Louis XVI period, circa 1785. © La Pendulerie – Agence**

**Fig. 11 – Porcelain and gilt bronze clock, case by the Queen’s Manufactory, movement by François-Louis Godon. Paris, Louis XVI period, circa 1785. © La Pendulerie – Agence**

Another rival of Sèvres was the factory owned by Christophe Erasimus Dihl and the Guérhards, which was known as the “Manufactory of the Duke d’Angoulême”. The duke became the factory’s patron in 1781. Toward the end of the reign of Louis XVI, the manufactory offered extraordinary groups and figures in bisque porcelain (i.e. unglazed), which were often mounted as clocks (fig. 12). For these pieces, the factory collaborated with the finest artisans, such as the enamel dial painter Joseph Coteau and Jean-Nicolas Schmit (d. circa 1820) who produced almost all of their movements (fig. 13).

Fig. 12 – Bisque porcelain and gilt bronze mantel clock, Dihl and Guérhard manufactory, known as the Duke d’Angoulême’s Manufactory, Paris, late Louis XVI period, circa 1790. © La Pendulerie – Agence

Fig. 13 – Bisque porcelain and gilt bronze mantel clock (detail), Dihl and Guérhard Manufactory, known as the Duke d’Angoulême’s Manufactory, movement by Jean-Nicolas Schmit, Paris, late Louis XVI period, 1785-1790. The dial bears the inscription “*Manuf.re de M.gr le Duc d’Angoulême/Schmit à Paris*”. © La Pendulerie – Agence

Conclusion

Porcelain clocks count among the most prestigious horological items made in Paris during the second part of the 18^th century. They were especially popular during the reign of Louis XVI. Whether they took the form of vases, lyres, or mounted plaques, new models appeared in rapid succession, bearing witness to the creative vision of the most talented artists and artisans. From the royal family to influential aristocrats, the excellent taste of the most sophisticated collectors influenced the style and design of these magnificent clocks. Gilt bronze mounts often served to highlight the beauty and delicacy of the porcelain.

While the production of the Royal Sèvres Manufactory is marked by a great diversity of shapes and decorations, it was also rivalled by private manufactories. This was the case for the factories known as “the Queen’s Manufactory” and “the Duke d’Angoulême’s Manufactory”, both of which produced equally remarkable porcelain clocks.

Y. Huang

Author: lapendulerie-admin

Understanding Precision Regulators: Technical Development of the 18th Century